1. Field of the Invention
The present invention relates to a driving force control device for a vehicle, which is configured to control driving forces to be generated on wheels so that a sprung vibration can be suppressed.
2. Description of the Related Art
Hitherto, there has been known a driving force control device configured to control driving forces to be generated on wheels, to thereby suppress a vibration of a vehicle body, namely, a sprung vibration. Control of suppressing the sprung vibration is referred to as sprung vibration damping control. When the sprung vibration damping control is carried out, the driving force control device calculates a vibration suppression torque, which acts in a direction of suppressing the sprung vibration (e.g., a pitch vibration of the vehicle body), sets a target torque acquired by adding the vibration suppression torque to a driver required torque, and controls a driving torque, which is generated by a drive device, in accordance with the target torque.
When this sprung vibration damping control is carried out, particularly in a drive device small in a torque capacity, e.g., a drive device used for a small vehicle, a required value required in the sprung vibration damping control may not be accepted, and a limit may thus be imposed on the vibration suppression torque. For example, in a drive device including a gasoline engine small in the displacement, a ratio of the vibration suppression torque to the driving torque that can be generated by the engine is high, and an opening degree change amount of a throttle for suppressing the sprung vibration is thus large. This large change may adversely affect basic control for the engine. Therefore, upper and lower limit values are set for the vibration suppression torque. On this occasion, a reason for using the expression of the upper and lower limit values is that the vibration suppression torque presents a waveform in which a driving force acting in a direction of increasing the driver required torque and a negative driving force (braking force) acting in a direction of decreasing the driver required torque alternately appear. Thus, the upper and lower limit values of the vibration suppression torque can be paraphrased as upper limit values of the respective absolute values of the driving torque acting in the direction of increasing the vibration suppression torque and the negative driving torque acting in the direction of decreasing the vibration suppression torque.
In this way, a technology of setting the upper and lower limit values of the vibration suppression torque is proposed in, for example, Japanese Patent Application Laid-open No. 2011-17303.
However, the setting of the upper and lower limit values of the vibration suppression torque may result in a state where the sprung vibration damping control performance cannot be sufficiently exerted.